mcmurdo 36-001-001A, Service Manual

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C1 S-VDR service manual Issue 1 Page 13
3.3 Message read
Part of the IMO requirement is that the SBM provider verifies the message. This can
be done with a "Message Reader". A typical instrument is the ARG5410. This model
will be used to describe the process. Operation of the Reader is detailed in its
handbook and will not be repeated here.
The procedure is as follows:
1. On the Reader select RECV mode
2. Position the Reader approx. 1m (3 feet) from the FFC
3. Perform a self test on the FFC
4. After about 12 seconds the 121.5MHz detector should emit three bursts of
sound
This proves the 121.5MHz homer is radiating and modulating correctly.
5. The Reader should beep and report S’TEST OK
6. The Reader will revert to its Menu. Select VIEW mode
7. Use
← →
keys to view the decoded 406MHz message content
8. Confirm the frequency was within 406.020 – 406.030
This proves the 406MHz transmitter is radiating within the correct frequency band. If
the ARG5410 Reader is not used, then another facility for measuring the 406MHz
frequency must be provided (a spectrum analyser for example).
9. Confirm the 15 digit ID agrees with FFC identity label UIN
This proves the 406MHz transmitter is modulating correctly and the EPIRB is
programmed with the correct vessel identity. If the ARG5410 is not used then another
facility for message decoding must be provided (other message readers).
10. Confirm the Flag state and the Serial No / MMSI / Callsign agrees
Typical screen
Q
11:25
Mesg#11 S’TEST OK
ID: 9D0D071D3B00013
406.0257 MHz PASS
Common problems
Audio tone If not heard then reduce range from 1m to 0.3m to help.
Frequency If outside limits, repeat the self test two or three times in
rapid succession to provide a warm up time. Repeat test.
Bad frame This error message occurs if the Reader fails to
synchronize.
This occurs approx. 10% of the time. Repeat test
multiple times. If EPIRB achieves <30% bad frames then
it is acceptable.
Also note that an exhausted reader battery causes bad frames.
Normal mode
It is possible to message read in live mode provided the EPIRB is in a screened
enclosure. In this case the Reader reports NORMAL OK and the first 3 bytes of the
full hex message are FF FE 2F… instead of the FF FE D0… for self test mode.